SYSTEMS AND METHODS FOR RESIN FLOW FRONT DETECTION IN HIGH-PRESSURE RESIN INJECTION MOLDING OF COMPOSITE PARTS

Abstract

A system and a method for forming a fiber-reinforced composite part are disclosed. The system comprises a mold with electrical contacts that establish an electrical connection with at least one monitoring circuit integrated into a fiber preform arranged in the mold, such that the resistance of the monitoring circuit can be monitored as resin fills the mold cavity and surrounds the preform. The method comprises monitoring the resistance of at least one monitoring circuit integrated into a fiber preform arranged in a mold to determine the location of the resin flow front as resin is injected into the mold and surrounds the fiber preform.

Description

INTRODUCTION

[0001] The information provided in this section is intended to provide a general context for the disclosure. Work by the presently named inventors, to the extent described in this section, as well as aspects of the description that may not be prior art at the time of filing, are neither expressly nor impliedly acknowledged as prior art to the present disclosure.

[0002] This disclosure relates to systems and methods for molding composite parts, and more particularly to systems and methods for resin flow front detection in high pressure resin injection molding of composite parts.

[0003] Some processes for molding composite parts involve injecting resin into a mold cavity containing a fiber preform. Because the mold is enclosed, the extent of resin fill can be difficult to determine, so the scrap rate can be relatively high. SUMMARY

[0004] Embodiments of this disclosure provide systems for resin flow front detection in resin injection molding of composite parts. According to a first embodiment, the system comprises a sub-mold having a plurality of mold sections operable between an open configuration and an operative configuration in which the mold sections form a mold cavity with an inner surface substantially having the shape of the composite part. Preferably, at least one set of electrical contacts is provided on the surface of the mold cavity for making electrical contact with at least one monitoring circuit that can be positioned within the mold cavity. This monitoring circuit can be integrated into a fiber composite sub-preform that can be placed within the mold cavity prior to resin injection, but is electrically isolated therefrom.An electrical resistance measuring circuit may be connected to the at least one set of electrical contacts on the mold surface to measure the electrical resistance of the at least one monitoring circuit in the mold cavity connected to the set of electrical contacts on the surface of the mold cavity.

[0005] It has been shown that the resistance of the monitoring circuits changes when resin is injected into the mold cavity and comes into contact with the monitoring circuits. The change in the resistance of the monitoring circuits, together with information about the mold cavity geometry, the resin flow path, and the resin properties, allows the location of a resin flow front to be determined during resin injection molding of composite parts.

[0006] According to a second embodiment of this disclosure, the system comprises a part mold and a fiber part preform disposed therein. The mold may comprise a plurality of mold sections that together form an internal mold cavity having a surface substantially corresponding to the shape of a composite part to be manufactured. The part mold may have at least one set of electrical contacts on the internal surface of the part mold. A fiber preform for the composite part is disposed within the mold cavity and includes a plurality of reinforcing fibers and at least one monitoring circuit whose resistance changes when the circuit is encased in resin.The at least one monitoring circuit has electrical contacts positioned on the preform such that when the preform is properly seated in the mold cavity and the mold is closed, the set of electrical contacts on the partial mold comes into contact with the electrical contacts on the at least one monitoring circuit.

[0007] When the electrical contacts on the monitoring circuit in the fiber preform are in electrical contact with the at least one set of contacts on the surface of the mold, the electrical resistance of the at least one monitoring circuit can be measured across the at least one set of electrical contacts on the surface of the mold. The change in the resistance of the monitoring circuits, along with information about the mold cavity geometry, the resin flow path, and the resin properties, enables the location of a resin flow front to be determined during resin injection molding of composite parts.

[0008] Embodiments of this disclosure also provide methods for resin injection molding of composite parts, and more particularly, methods for resin flow front detection in resin injection molding of composite parts. According to a third embodiment of this disclosure, a method for molding a composite part comprises inserting a partial preform into a mold cavity. The preform includes at least one monitoring circuit whose resistance changes when surrounded by resin. The method further comprises injecting resin into the mold under pressure and measuring the resistance of the monitoring circuit while the resin is injected. The location of the resin flow front can then be estimated based at least in part on the measured resistance of the monitoring circuit.Optionally, one or more molding process parameters can be adjusted based on the estimated resin flow front in the mold resulting from the measured resistance data. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present disclosure will be more fully understood from the detailed description and the accompanying drawings, in which: Fig. Figure 1 is a schematic representation of a composite part preform in a mold while resin is injected into the mold; Fig. 2 is a schematic representation of a composite part preform in a mold while resin is injected into the mold, as in Fig. 1 shown after additional resin was injected into the mold; Fig. 3 is a schematic representation of a composite part preform in a mold while resin is injected into the mold, as in Fig. 2 shown after additional resin was injected into the mold; Fig. 4 is a schematic representation of a composite part preform in a mold while resin is injected into the mold, as in Fig. 3 shown after additional resin has been injected into the mold; Fig. Figure 5 is a schematic representation of a composite part preform in a mold while resin is injected into the mold; Fig. 6 is a schematic representation of a composite part preform in a mold while resin is injected into the mold, as in Fig. 5 after additional resin has been injected into the mold; Fig. Figure 7 is a schematic representation of a composite part preform in a mold while resin is injected into the mold, as in Fig. 6 after additional resin has been injected into the mold; Fig. Figure 8 is a schematic representation of a composite part preform in a mold while resin is injected into the mold; Fig. 9 is a schematic representation of a composite part preform in a mold while resin is injected into the mold, as in Fig. 8 after additional resin has been injected into the mold; Fig. 10 is a schematic representation of a composite part preform in a mold while resin is injected into the mold, as in Fig. 9 after additional resin has been injected into the mold; Fig. 11 is a schematic diagram illustrating the layers assembled to produce a partial preform in accordance with the principles of this disclosure; Fig. Figure 12 is a schematic diagram of the composite layers being aligned with a preforming tool; Fig. 13 is a schematic representation of the composite layers formed by the preforming tool; Fig. 14 is a schematic diagram illustrating the finished preform in the preforming tool; Fig. Figure 15 is a side elevation view of the finished preform; Fig. Figure 16 is a schematic view of a partial preform seated in the lower portion of an open mold; Fig. Figure 17 is a schematic view of a partial preform seated in a closed mold and ready for resin injection; Fig. Figure 18 is a schematic view of a finished part in a closed mold; Fig. Figure 19 is a schematic view of a finished part in an open mold; Fig. 20 is a schematic view of a monitoring circuit integrated into a preform, the configuration of the circuit varying across the preform to allow increased resolution of the location of the resin flow front towards the end of the fill cycle; and Fig. Figure 21 is a schematic view of a plurality of monitoring circuits arranged in an overlapping manner to enable finer resolution of the location of the resin flow front during filling.

[0010] Reference numerals may be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0011] Embodiments of this disclosure provide systems for resin flow front detection during resin injection molding of composite parts. A system according to a first embodiment of this disclosure is described in Fig. 16-19 generally designated 20. The system 20 includes a partial mold 22 having a plurality of mold sections 22 and 24 that can be configured between an open configuration ( Fig. 16, Fig. 19) and an operating or closed configuration ( Fig. 17, Fig. 18), wherein the mold sections form a mold cavity with an inner surface substantially having the shape of the composite part. To ensure complete forming of the part, the mold may intentionally include excess volumes to accommodate overfill, portions of which may be trimmed off to form the final part.

[0012] Preferably, at least one set of electrical contacts 26, 28 is provided on the inner surface of the mold cavity for establishing electrical contact with at least one monitoring circuit that may be positioned within the mold cavity. This monitoring circuit may be integrated into a fiber composite preform 32 that may be placed within the mold cavity prior to resin injection, but is electrically isolated from it.

[0013] An electrical resistance measuring circuit 30 can be connected to the at least one set of electrical contacts 34, 36 to measure the electrical resistance of the monitoring circuit in the mold cavity, which is connected to the set of electrical contacts 26, 28 on the surface of the mold cavity. It has been found that the resistance of the monitoring circuits changes when resin is injected into the mold cavity and comes into contact with the monitoring circuits. In at least some embodiments, the change (reduction) in resistance is the result of portions of the monitoring circuit being shorted by the injected resin surrounding portions of the monitoring circuit.The change in resistance of the monitoring circuits, alone or in combination with other data such as information about the mold cavity geometry and orientation, and the resin flow path and properties, enables the determination of the location of a resin flow front during resin injection molding of composite parts.

[0014] The production of the partial preform 32 is in Fig. 11-15. As shown in Fig. 11, a plurality of layers are assembled. The layers may include carbon fiber mats or scrims 40 and 42, a layer 44 comprising a monitoring circuit 30, and layers 46 and 48 for electrically isolating the monitoring circuit from the conductive carbon fiber layers to ensure that changes in the resistance of the monitoring circuit are due to the presence of resin and not to contact with other support layers. The five layers are merely illustrative of one possible construction, and the actual preform may include additional layers and layers of various materials suitable for the finished part. For example, the layers may also include other materials such as glass fibers, polymers, or other suitable materials.

[0015] As in Fig. 12, the layers for the preform are aligned with a preforming tool 50, which consists of an upper and lower part, which, as shown in Fig. 13, to compress the layers together. The layers may be held together mechanically by deforming the layers, or binders may be used to keep the layers together and / or help the preform maintain its desired shape. These binders may be chemically activated, heat activated, or photoactivated. As part of the manufacture of the preform 32, electrical contacts, such as contacts 34, 36, may be formed in or on the surface of the preform that are in electrical communication with the at least one monitoring circuit. When multiple monitoring circuits are present, each preferably has its own electrical contacts so that the resistance changes of each monitoring circuit can be measured separately.The preform tool 50 preferably assists in correctly positioning the electrical contacts on the preform 32 during assembly so that the contacts on the preform are aligned with the corresponding contact sets on the mold sections when the preform is properly inserted into the corresponding mold.

[0016] According to a second embodiment of this disclosure, the system includes a sub-mold 20 and a fiber sub-preform 32 disposed therein. The mold may include a plurality of mold sections, e.g., sections 22 and 24, which together form an internal mold cavity having a surface substantially corresponding to the shape of a composite part to be manufactured. The sub-mold 20 may have at least one set of electrical contacts 26, 28 on the inner surface of the sub-mold. A fiber preform 32 for the composite part is disposed within the mold cavity and includes a plurality of reinforcing fibers and at least one monitoring circuit 30 whose resistance changes when surrounded by resin.

[0017] The at least one monitoring circuit 30 may be made of a metal or metal alloy, or of carbon fiber, or another material that provides a measurable resistance within a suitable range. The resistance of the monitoring circuit 30 changes when surrounded by resin, which may itself be electrically conductive, so that the reduction in resistance when the resin shorts the path of the monitoring circuit 30 indicates the location of the resin flow front. The monitoring circuit has electrical contacts 34, 36 positioned on the preform 32 so that, when the preform is properly seated in the mold cavity and the mold is closed, the set of electrical contacts 26, 28 on the partial mold comes into contact with the electrical contacts 34, 36 on the at least one monitoring circuit. Multiple monitoring circuits 30 may be provided in the preform, as shown in Fig. 20 and Fig. 21, and the electrical contacts of these circuits and the mold are arranged so that the resistance in each of the circuits 30 can be monitored separately.

[0018] When the electrical contacts 34, 36 on the monitoring circuit 30 are in electrical contact with the at least one set of contacts 26, 28 on the surface of the mold, the electrical resistance of the at least one monitoring circuit can be measured across the at least one set of electrical contacts on the mold. The change in the resistance of the monitoring circuits 30, along with information about the mold cavity geometry and the resin flow path and properties, enables the location of the resin flow front to be determined during resin injection molding of composite parts.

[0019] Embodiments of this disclosure also provide methods for resin injection molding of composite parts, and more particularly, methods for resin flow front detection during resin injection molding of composite parts. According to a third embodiment of this disclosure, a method for molding a composite part includes inserting a partial preform 32 into a cavity of a mold 20. The preform includes at least one monitoring circuit 30 whose resistance changes when surrounded by resin. The method further includes injecting resin into the mold 20 under pressure and measuring the resistance of the monitoring circuit or circuits 30 while the resin is injected. The location of the resin flow front during injection can then be estimated based at least in part on the measured resistance of the monitoring circuit.Optionally, one or more molding process parameters such as resin injection pressure, identity of injection locations used, volume of injected resin based on resin flow front feedback can be provided.

[0020] The functioning of the system and the procedure are described in Fig. 1-4 illustrates where a preform 32 is shown with a monitoring circuit 30 having a generally serpentine configuration. As in Fig. 1, if the resin flow front 60 has not reached the circuit 30, the resistance of the circuit remains unchanged, indicating that the front has not reached the circuit location. As shown in Fig. 2, as soon as the resin flow front reaches the circuit 30, parts of the circuit are short-circuited, thereby reducing the resistance of the circuit and indicating that the resin flow front 60 has advanced beyond the circuit 30. As shown in Fig. 3, an even larger portion of the circuit 30 was short-circuited, with a corresponding reduction in resistance, indicating the more advanced position of the resin flow front 60. Finally, the resin in Fig. 4 has advanced even further, has short-circuited an even larger part of the circuit than in Fig. 3 and indicates that the filling of the mold is almost complete and that the resin flow front 60 has almost completely penetrated the circuit.

[0021] Similarly, the operation of the system and the method in Fig. 5-7 illustrates where a partial preform 32 includes a spiral-shaped monitoring circuit 30. The injection point in this example is in the center of the spiral. As in Fig. As shown in Figure 5, when resin injection begins, the resin begins to surround the center of the coil, shorting the section of the circuit in the center of the coil and reducing the overall resistance of the circuit. This indicates that the resin flow front is still near the center of the circuit (and the center of the preform in the mold). As shown in Fig. 6, the continued filling of the mold cavity causes the resin flow front 60 to move outward from the center of the mold cavity, thereby shorting more of the monitoring circuit 30, reducing the measured resistance of the monitoring circuit, and indicating that the resin flow front is located between the center and the outer edge of the circuit. In Fig. 7, the resin flow front 60 has advanced even further, and the corresponding reduction in resistance indicates that the resin flow front 60 is adjacent to the outer edge of the circuit.

[0022] Similarly, the operation of the system and the method in Fig. 8-10 illustrates where a partial preform 32 includes four monitoring circuits 30. The injection point of the resin in this example is in the center of the preform 32. As in Fig. As shown in Figure 8, before the start of injection, the resistance of the circuits is unchanged, indicating that the injection has not yet started or at least has not progressed far. Fig. 9, the resin flow front 60 has advanced far enough to reach each of the circuits 30, thereby reducing the resistance of each circuit. This indicates that the resin flow front is still near the center of the circuit (and the center of the preform in the mold). As shown in Fig. As shown in Figure 9, the continued filling of the mold cavity causes the resin flow front 60 to move outward from the center of the mold cavity, thereby shorting more of the monitoring circuits 30, reducing the measured resistance of the circuit, and indicating that the resin flow front is located between the center and outer edge of the preform. The relative changes in the resistances in the four monitoring circuits indicate the shape of the resin flow front 60. Fig. 10, the resin flow front 60 has advanced even further toward the edges of the preform 32, and the corresponding reduction in the resistances in the four monitoring circuits 30 indicates that the resin flow front 60 is closer to the outer edge of the circuits and the preform.

[0023] As in Fig. 20, the shape of the monitoring circuit 30 may vary, in this case with an increasing number of more closely spaced loops to provide finer resolution of the resin flow front as the resin fills the cavity from left to right, as shown in the figure.

[0024] As in Fig. 21, a plurality of monitoring circuits 30 may be arranged in an overlapping manner to provide fine resolution of the position of the resin flow front, in this case as the resin flows into the mold and over the preform 32 from right to left.

[0025] The foregoing description is merely illustrative and is not intended to limit the disclosure, its application, or uses in any way. The broad teachings of the disclosure may be embodied in a variety of forms. Therefore, while this disclosure includes specific examples, the true scope of the disclosure should not be limited thereto, since other changes will become apparent upon study of the drawings, the patent specification, and the following claims. It is understood that one or more steps within a method may be performed in a different order (or simultaneously) without altering the principles of the present disclosure.Furthermore, although the embodiments are each described above as having specific features, any one or more of these features described with respect to one embodiment of the disclosure may be implemented and / or combined with features of any of the other embodiments, even if this combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and interchanging one or more embodiments remains within the scope of this disclosure.

[0026] Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaging," "coupled," "adjacent," "beside," "on top of," "over," "below," and "disposed." Where a relationship between first and second elements is not explicitly described as "direct" in the above disclosure, that relationship may be a direct relationship, with no other intervening elements between the first and second elements, or an indirect relationship, with one or more intervening elements (either spatial or functional) between the first and second elements.As used herein, the term “A, B and / or C” should be construed as logical (A ORed with B ORed with C) using a non-exclusive logical OR and should not be understood as “at least one of A, at least one of B and at least one of C”.

Claims

[1] System for manufacturing composite parts, the system comprising: a part mold having a plurality of mold sections operable between an open configuration and an operative configuration in which the mold sections form a mold cavity having a surface substantially conforming to the shape of the composite part; at least one set of electrical contacts on the surface of the mold cavity for making electrical contact with a monitoring circuit positioned within the mold cavity; at least one electrical resistance monitoring circuit electrically connected to the at least one set of electrical contacts on the surface of the mold cavity for measuring the electrical resistance of the at least one monitoring circuit connected to the at least one set of electrical contacts on the surface of the mold cavity; and a processor for estimating a location of a flow front of the resin injected into the mold cavity based at least in part on electrical resistance measurements of the at least one monitoring circuit. [2] The system of claim 1, wherein the at least one monitoring circuit is integrated into a reinforcement preform disposed in the mold. [3] The system of claim 2, wherein the fiber reinforcement preform comprises barrier layers that electrically isolate the at least one monitoring circuit from the fiber reinforcement preform. [4] The system of claim 2, wherein a plurality of monitoring circuits are integrated into the fiber reinforcement preform. [5] The system of claim 4, wherein portions of a plurality of monitoring circuits overlap. [6] A method of forming a fiber-reinforced composite part, the method comprising the steps of: Inserting a fiber preform into a mold cavity, the preform comprising at least one monitoring circuit whose resistance changes when surrounded by resin; Injecting resin into the mold under pressure; Measuring the resistance of the at least one monitoring circuit; and Estimating the location of a resin flow front in the mold using the measured resistivity data. [7] The method of claim 6, further comprising changing at least one parameter of the molding process depending on the estimated location of a resin flow front. [8] The method of claim 6, wherein the mold includes at least first and second electrical contacts, and wherein the at least one monitoring circuit includes first and second electrical contacts positioned on the preform to engage the first and second electrical contacts on the mold, and wherein the resistance of the monitoring circuit is measured by measuring the electrical resistance between the first and second electrical contacts on the mold. [9] The method of claim 6, wherein the fiber preform comprises a plurality of monitoring circuits. [10] The method of claim 9, wherein at least some of the plurality of monitoring circuits at least partially overlap.

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